This invention relates to the transfer of a small amount of liquid medium from a first position to a second position. Particularly, the invention relates to the transfer of a fluid droplet from a sample source to a surface. More specifically, the invention relates to a transfer loop that can release a fluid a droplet onto a surface in a non-random manner.
Over the years the fields of clinical biochemical analysis, microbiological analysis, virological analysis, forensic and chemical analysis in general have seen a massive surge in diagnostic and chemical assay methods that enable fast and rapid analysis of numerous parameters. Concomitant with this rapid pace of development has been the parallel development of small sample analysis wherein qualitative analysis and in some cases precise quantitative analysis may be performed on a fluid droplet or aliquot of fluid. For example, a pregnancy test kit and a HIV qualitative test kit require only a small sample to detect the presence of biological markers that indicate a pregnancy or a HIV infection, respectively.
There has also been a growing demand for rapid testing. For example, the physician or physician's assistant might collect a blood or urine sample and immediately analyze the sample in the doctor's surgery without need to transfer the sample to a central laboratory for independent analysis. The patient gets their test result quickly and the physician has more control over the whole process. There has been an explosive growth in demand for home test kits such as personal pregnancy test kits. Likewise, diabetics have benefited from the development of small test kits that can measure blood glucose levels based on the analysis of a single droplet of blood. Home patients, for example kidney dialysis patients, benefit from the ease with which bodily fluid samples such as blood and urine might be tested using a home test kit. Home test kits often involve handling an aliquot of fluid. Thus there is a demand for a simple way of transferring an aliquot of fluid from a sample site to the test kit.
Out in the field, technicians, industrial chemists, field biologists, industrial microbiologists, and engineers sometimes need to test various systems without having to waste time trekking samples back to the laboratory for analysis. For example, a water biologist or chemist might need to check for the presence of a specific pesticide in a river or stream that feeds a fresh water reservoir. Testing for a particular bacterium such as E. coli in seawater alongside tourist beaches might also be of interest to an environmentalist. The field scientist, technician, physician, nurse, environmental activist, Environmental Protection Agency ("EPA") Inspector, field engineer, home patient, or research student might take a sample in the form of an aliquot of fluid and deposit the aliquot of fluid on a test surface for analysis.
The conditions for field scientists and field engineers are frequently not ideal. Cold and damp hands might make transferring aliquots of fluid or fluid droplets from a sample source to a test surface difficult and haphazard. Likewise the physician or physician's assistant is sometimes under pressure and needs a simple means to transfer, for example, an aliquot of blood from a bleed site to a test surface. Further, the advent of home test kits and their use by largely unskilled adults increases the chances of mishap in transferring an aliquot of fluid, such as a droplet of blood from a lanced finger or a droplet of urine, to a test surface for analysis. Thus there is a need for a simple transfer device that transfers an aliquot of fluid from a sample site to a test surface.
A Pasteur pipette might be used to transfer a small droplet of fluid from the sample source to a test surface. For example, a Pasteur pipette might be used to transfer an aliquot of blood from a bleed site on a lanced finger to a test surface. However, the basic operation of the Pasteur pipette relies on a pumping action wherein an elastic rubber or plastic teat is pressed between the thumb and index finger to create a partial vacuum. The blood droplet may then be sucked into the mouth of the Pasteur pipette and thence into the stem of the pipette by slowly releasing the teat. The droplet is then dispensed onto the test surface by a controlled squirting action upon pressing the teat between the index finger and thumb. Even with expert use of finger and thumb it is possible to generate a small aerosol spray of blood leading to an accidental inhalation risk. The contact surface might include a well into which the pipette could be inserted prior to expulsion of the blood droplet. While the use of a well would decrease the likelihood of accidental inhalation of blood mist, the physician or physician's assistant may still accidentally release at least part of the aliquot of blood from the pipette prior to successfully inserting the mouth of the pipette into the well. The Pasteur pipette is a potential health hazard when it is in unskilled hands. Specifically, anyone in close proximity to an inexpertly used Pasteur pipette is presented with an inhalation risk.
The blood droplet may be transferred from the surface of the finger to the test surface by means of a static transfer device such as a glass rod. However, there is a risk of the blood droplet falling from the rod and causing blood splatter on impact with the floor or other surface. This presents a safety hazard to the physician, nurse or other medical professional. Alternatively the blood droplet may be transferred from the finger by directly smearing the finger onto the test surface. This might be undesirable because the test surface might contain test reagents that should not come into direct contact with the skin of a patient.
A loop may be used to transfer a fluid droplet such as a droplet of blood. Various transfer loops, including bacteriological transfer loops, are described in the literature. For example, U.S. Pat. No. 4,010,077 describes an improved bacteriological transfer loop for use in bacteriological identification. However, such loops of the prior art require a streaking action in order to effect transfer.
U. S. Pat. No. 3,147,197 describes a bacteriological transfer loop for transferring liquid medium from one culture medium to another. Such transfer loops of the prior art are frequently problematic when used to transfer an aliquot of fluid from a sample source to a specific location on a surface. To initiate the release of the fluid droplet, the loop might have to be angled or flattened against the surface. This often causes a problem because the aliquot of fluid appears to have a mind of its own and will sometimes not transfer from the loop to a specific location on a surface. Flattening the loop against the surface may cause damage to a sensitive test surface when the test surface comprises a matrix that is sensitive to pressure or excessive contact with a loop. Thus there is a need for a transfer loop that does not require much effort on the part of the operator to cause the release of a fluid droplet onto a surface. In addition, aligning or flattening the loop relative to the surface can lead to undesirable consequences wherein the fluid droplet is transferred in a somewhat random manner onto a surface. Using a well with walls that define a small radius might help to ensure that the fluid droplet is placed where it is needed. However, the deeper the well the less the operator can bend or flex the loop relative to the surface because the stem of the loop will contact the sides of the well. Also, it is hard to see if the droplet has in fact been deposited onto the surface. Hence there is a need for a transfer loop that can release a fluid droplet onto a surface in a non-random manner.